German Offenlegungsschrift 33 28 376 discloses inter alia the 5-hydroxydiprafenone, i.e. the 2-[2'-hydroxy-3'-(1,1-dimethylpropylamino)-propoxy]-5-hydroxy-.beta.-pheny lpropiophenone having the following formula I: ##STR1##
The preparation of this compound is carried out by using the correspondingly substituted acetophenone, i.e. 2,5-dihydroxy acetophenone, which after etherification of the phenolic hydroxyl group in position 2 with benzyl bromide (yield approx. 72%) which is reacted with benzaldehyde to form the corresponding .alpha.,.beta.-unsaturated ketone, i.e. 5-benzyloxy-2-hydroxy-benzalacetophenone (yield approx. 57%). This compound is reacted in almost quantitative yield with epichlorohydrine to form 2-(2',3'-epoxypropoxy)-5-benzyloxy-benzalacetophenone and then with 1,1-dimethylpropylamine to form 2-[2'-hydroxy-3'-(1,1-dimethylpropylamino)-propoxy]-5-benzyloxybenzalaceto phenone. Subsequently, the 5-hydroxydiprafenone is obtained in a yield of approx. 17% of the theoretical value by catalytic hydrogenation in the presence of palladium-on-carbon (10%). The total yield of this multi-step process is about 7%. This process is not suitable for the preparation of 5-hydroxydiprafenone on an industrial scale as it is dependent on 2,5-dihydroxyacetophenone which is prepared only with a poor yield and therefore is comparatively expensive. The acylation of hydroquinone according to Friedel-Crafts results preferably in the formation of the phenolic esters.